Detinning of tinned iron-scrap



M. A. ADAM, J. STEVENSON AND A. T. MABBITT.

DETINNING OF TINNED mow SCRAP.

APPLICATION FILED AUG.3I,1920

Patented. May 24, 1921.

UNITED; STATES PATENT OFFICE.

MATTHEW ATKINSON ADAM, JOHN STEVENSON, AND ALAN THOMAS MAYBIBIT'I, 0F LQNDON, ENGLAND; SAID STEVENSON AND SAID MABIBI'IT ASSIGNURS T0 SAID ADAM.

DETINNING 01* TINNED IBQN-SCRAP.

T 0 all whom it may concern:

Be it known that we, MATTHEW ATKINSON ADAM, residing at 57, Lincolns Inn Fields, London, W. C. 2, England, JoHN STEvnNsoN,

residing at 28 Talbot road, Bayswater, Lo'ndon, W. 2, England, and ALAN THoMAs MABBITT, residing at 3 Wallwood road, London, E. 11, England, all subjects of the King of Great Britain and Ireland, have invented certain new and useful Improvements Relating to the Detinning of Tinned Tron- Scrap, of which the following is a specification.

This invention relates to the recovery of tin in the wet way from tinned iron, 6. 9., tin plate scrap.

lit has hitherto been proposed to use strong boiling solutions of ferric chlorid to dissolve tin from tinned iron scrap, and then after adding phenol and sulfuric acid to the drawn off solution, to electrolyze the same. A lead cathode and a cloth covered anode were proposed, and the separated tin was proposed to be collected at the bottom of the electrolyte. (See Ramos Garcia, British Patent No. 18726 of 1890.)

In this process as described, filtering of the solution was employed, and regeneration of the dissolving. fluid effected by the addition of ferric chlorid crystals intermittently collected and utilized after volatilizetion. Also, owing to the additions used for electrolysis, the solution could not be employed over again without treatment.

More recently weak solutions of ferric chlorid and hydrochloric acid have been tried on an industrial scale to recover tin from tinned. iron scrap by dissolving tin and afterward .depositing tin from the solution by electrolysis in separate cells with stationary cathodes; the solution being circulated very slowly through the electrolytic cells. Considerable diificultieshave arisen in the industrial utilization of this type of process, inter alia, owing to the slow rate of solution of the tin, and to the fact that the yield of tin in the electrolysis of the solutions does not approach in practice even the equivalent corresponding to stannic chlorid.

The object of the present invention is to provide an improved process according to which both a rapid rate of solution and a rapid rate of recovery of tin may be efl'ected Specification of Letters Patent.

so thata continuous process on a commercial scale is provided.

Patented llfay 24;, 1921.

Application filed. August 31, ,1920. Serial No. 407,250.

The invention consists, in brief, in employing strong solutions of the chlorids of tin and iron, with or withouta small per centage of added hydrochloric acid' for dissolving the tin from the tinned iron scrap, and circulating the solution through one or more electrolytic cells operating at high current densitiesfrom which the deposit is automatically removed, and preferably removing by electrolysis only about the same amount of tin as has been dissolved in the scrap treatment. 3 1

lln carrying the invention into effect in one form by way of example, we make a solution in Water of ferric chlorid to 'a strength of about 25%, adding about 1% hydrochloric acid. We then introduce metallic tin and permit this to be dissolved as far as practicable, viz., until the solution contains About 6-% stannous chlorid, and

About 1%-% stannic chlorid.

The ferric chlorid often contains some free hydrochloric acid, so the amount of hydrochloric acid added varies to a certain eX-- tent, but we prefer only to add such an amount that the total free acid in the mixture is not greater than say 3%. The solution resulting from the above mixture (which consists substantially of ferrous, stannous and stannic chlorids and hydrochloric acid) is employed for removing the tin from the tin scrap, and we find it dissolved tin well at ordinary atmospheric tem-- peratures from such scrap, and attacks iron but little.

After solution of the tin, the liquor 1s electrolyzed as explained below, and the effluent rapidly, then the solution is sufliciently active for practical work for dissolving the tin from the tin plate when it contains say about 8% of tin chlorids as indicated above, part being in the stannous and part in the stannic form (although as regards the tin salts, only the stannic chlorid is available for the solution of tin, it being converted to stannous chlorid by the reaction). The liquor made as above described may be regarded as saturated with tin from the aspect of the solvent in question, that is to say, if a 25% ferric chlorid solution be allowed to take up as much metallic tin as is practicable, that is, until the resulting liquor contains tin chlorids to approximately the extent described above, the liquor can be used to dissolve tin from tin plate by the action of the stannic chlorid content. It is desirable from the electrolytic point of view to keep the tin content of the solution as high as possible (so that the ratio of stannous to stannic tin is high) but from the point of view of dissolving tin from tin scrap it is desirable to keep some way from the saturation point in order to secure sufliciently rapid working.

In the electrolysis we prefer so to choose the rate of (a) relative movement between the cathode surface and the electrolyte, e. 9., the speed of rotation of the cathode, (b) liquid flow, and (0) current density, that only a comparatively small amount of the total tin content is deposited from the solution as explained above, and that it is deposited in a non-coherent form.

We have found that good results are obtained with a current density of about 450 amperes per square foot in a cell in which the cathode is rotated at a peripheral speed of about 10 inches per minute, the liquid flow being about 10 gallons per hour through a channel between anode and cathode of about s" x 6", and in this case the amount of tin deposited from the solution was about 0.2 lb. per hour. If it be desired to treat a different volume of liquid, this will determine the rate of liquid flow, and according to the quantity of metal it is required to deposit from the solution, so the current will be determined. In this way the cathode area is fixed, and the current density must be so chosen that a deposit suit- 1 able for removal by a light scraping action is obtained. The conditions may, however, be varied, e. 9., by depositing a larger proportion of tin from the solution. If the area of the cathode be fixed, then the rate of rotation should be such that a non-adherent deposit is obtained with the given current density. The rate of liquid flow and the size of the cell may be selected on the basis of the above figures according to the different conditions which may exist in matters under consideration, that is, for example, the different amount of liquid to be treated.

Referring to the accompanying diagrammatic drawings- Figure 1 represents a convenient arrangement of tanks and system-generally; and

Fig. 2 indicates a convenient construction of electrolytic cell.

In the arrangement illustrated, the scrap suspended in baskets say of metal openwork coated with acid-resisting enamel, is immersed in the dissolving solution and agitated therein in any suitable way as indicated by way of example in Fig. 1. Conveniently, the baskets a are suspended in pairs on the ends of a lever 7) supported from a carriage con a runway (Z. They thus balance one another, and are easily manipulated by hand or mechanically to secure an intimate contact of the scrap with the liquid. The carriage c is provided with raising and lowering gear 6, so that the baskets are raised after treatment in tanks f, g or 72,, moved along the runway to a pair of washing tanks 2', in which they are immersed in water, and again preferably to a limewater tank j, or to a copper-depositing tank in which a slight deposit of copper is made on the scrap to protect it from subsequent oxidation.

The store tank u is connected through piping o to the electrolytic cell is, after which it passes through a heater to to pipe 'a whence itmay be distributed to any pair of: tanks f, g or k at will.

The electrolytic cell k. we prefer to use is formed as a semi-circular trough in which is disposed a drum cathode of length about equal to that of the trough.

A form of construction of electrolytic cell is illustrated diagrammatically in Fig. 2, in which the trough is formed by a graphite bar Z hollowed out and provided with holes 172. along its bottom for exit of the electrolyte. The electrolyte passes into the trough cell from both sides n of the supply chamber over the edges of the graphite trough Z through the exit passages m into a sump o whence it flows through a number of ways p to the outlet pipe 9.

The graphite bar is preferably impregnated with paraflin wax to exclude the electrolyte from the pores thereof. Electrical connection may be made conveniently by copper rods 2 passing through the end of the cell and entering the cathode bar, care being taken that no access to this connection is possible by the electrolyte.

The drum cathode r is mounted upon a spindle above the trough Z, and thus may be rotated during action of the cell with part of its surface immersed in the electroyte, the latter being caused to flow at a steady rate through the system as determined by a cock t (Fig. 1). A scraper 3 is arranged to collect the metallic tin from the surface of the drum.

, In operation of the system one of the inlet cocks, say y, is opened and the cock I set to give the required rate of flow of the electrolyte. In the tanks f, when sufiiciently full, the baskets a are lowered for detinning, and the cock y closed, and, say .2, opened. Thus the flow of electrolyte is not disturbed, but merely now transferred to the tanks Similarly, when detinningis complete in tanks f, the appropriate outlet cock is opened, and the electrolyte returned to the store tank 14 by means say of a pump 1.

Having now described our invention,

what we claim as new and desire to secure by Letters Patent is: 1

1. A. process for the detinning of tinned iron scrap which consists in dissolving the tin in strong solutions of the chlorids of tin and iron approaching saturation and circulating the solution through an electrolytic cell operating at high current density and practically continuously removing the non-coherent deposit.

2. A process for the detinning of tinned iron scrap which consists in dissolving the tin in strong solutions of the chlorids of tin v and iron approaching saturation with a small percentage of added hydrochloric acid and circulating the solution through an electrolytic cell operating at high current density and practically continuously removing the non-coherent deposit.

3. A process for the detinning of tinner iron scrap which consists in dissolving the tin in strong solutions of the chlorids of tin and iron approaching saturation and circulating the solution through an electrolytic cell operating at high current density and practically continuously removing the noncoherent deposit, the solution employed being substantially saturated with tin throu hout the whole of the, process.

4-. g process for the detinning of tinned iron scrap which consists in dissolving the tin in strong solutions of the chlorids of tin the cathode surface and the electrolyte, e- 9-? the speed of rotation of the cathode, (7)) liquid flow. and (0) current density, being so adjusted that only a comparatively small amount of the total tin content is deposited from the solution, and that it is deposited in non-coherent form.

6. A process for the detinning o1 tinned iron scrap which consists in dissolving the tin in strong solutions of approximately 8% of the chlorids of j tin and approximately 25% of chlorids of iron and circulating the solution through an electrolytic cell operating at high current density and practically continuously removing the non-coherent deposit.

7. A. process for the detinning of tinned iron scrap which consists in'dissolving the tin in strong solutions of the chlorids of tin andiron approachin saturation and circulating the solution through an electrolytic cell operating at high current density and practically continuously removing only the tin dissolved from the tinned iron.

In testimony whereof we have signed our names to this specification.

MATTHEW ATKINSON ADAM. JOHN STEVENSON. ALAN THOMAS MABlBITT. 

